/*
 * Copyright 2011-2013 Blender Foundation
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include "stdosl.h"
#include "node_fresnel.h"

shader node_layer_weight(float Blend = 0.5,
                         normal Normal = N,
                         output float Fresnel = 0.0,
                         output float Facing = 0.0)
{
  float blend = Blend;
  float cosi = dot(I, Normal);

  /* Fresnel */
  float eta = max(1.0 - Blend, 1e-5);
  eta = backfacing() ? eta : 1.0 / eta;
  Fresnel = fresnel_dielectric_cos(cosi, eta);

  /* Facing */
  Facing = fabs(cosi);

  if (blend != 0.5) {
    blend = clamp(blend, 0.0, 1.0 - 1e-5);
    blend = (blend < 0.5) ? 2.0 * blend : 0.5 / (1.0 - blend);

    Facing = pow(Facing, blend);
  }

  Facing = 1.0 - Facing;
}
